I think it's the super sword "technique" you can buy with 100(?) carrots.
I saved up carrots just for this one, and it made the game so much easier, as you can cut through enemies from all sides then.
I never even needed any of the other items/techniques, except for the magic eye (that signposts secret passages).
Both these powerful items probably spoilt the whole experience as I completed Kung Fu Rabbit on the day I bought it in Normal Mode and Hardcore Rabbit Mode with all achievements and all items x 10. (5hrs and 30min total game time)
So with the right items equipped/bought early on this game is rather easy.